/dev/hda4 represents the 'extended' container partition to hold the
extended logical partitions like hda5.
I think /dev/shm is a new thing in 2.4.x. I am guessing it is for
'Shared Memory'.
A second HardDisk will show up as device hdb.
To partition use fdisk.
To format use mkfs.
Here is a detailed link:
http://www.redhat.com/docs/manuals/linux/RHL-7.3-Manual/ref-guide/s1-filesystem-ext3-create.html
Good Luck